LISTERIA-MONOCYTOGENES IN BOVINE MASTITIS - POSSIBLE IMPLICATION FOR HUMAN HEALTH

During the 23-year period 1972 through 1994 quarter milk samples from 1 132 958 cows originating from 36 199 herds were examined for the pre sence of Listeria monocytogenes. Through the period the reference popu lation amounted to 12 742 600 cow years and 401 682 herd years. The pe rcentage of cows infected with L. monocytogenes varied from 0.01 to 0. 1% (mean 0.04%) and of herds with an infected cow from 0.2 to 4.2% (me an 1.2%) through the period, showing a low but constant level of infec tion. A comparison of 33 isolates from bovine mastitis and 27 human cl inical isolates was made by sero- and ribotyping. Serotyping showed th at all bovine and 17 (63%) of the human isolates belonged to serogroup 1, whereas 10 (37%) of the human isolates belonged to serogroup 4. Ri botyping using EcoRI as restriction enzyme divided the 60 isolates int o 16 different types, 7 of which were Found among both the bovine and human types. The combination of the typing methods showed that 26 (79% ) bovine and 13 (48%) human isolates shared common types. This study s howed that a low but constant percentage of Danish dairy herds have co ws infected with L. monocytogenes and that some of the bovine types co uld be found among types causing human infections.